In x-ray computer tomography used for medical purposes, a special procedure is used to calculate a three-dimensional image of an object from normal x-ray images, which do not contain any kind of depth information since they represent a projection of a three-dimensional object onto a two-dimensional surface. In this procedure, in one rotation, an imaging unit—e.g. comprising an x-ray tube and an x-ray detector—is rotated through at least 180° around the object and between 50 and 1000 projection images of the object are recorded in small angular increments and the respective angles of projection, also known as recording angles, are stored. A three-dimensional data record of the object can be obtained from these numerous projection images and recording angles by using special algorithms, e.g. the so-called filtered back-projection or ART (Algebraic Reconstruction Technique). The totality of the projection images that originate from the same rotation are also referred to below as “rotation images”. Since projection images of which the angles of projection vary by 180° are mirror-symmetrical, the structure is captured completely by a rotation image around 180° (plus fanning angle of the x-ray tube).
This method is generally executed by means of specially constructed computer tomographs (CT devices).
For x-ray images in image-controlled diagnostic or surgical interventions on a patient, in which normal x-ray images are continuously recorded during the intervention, other x-ray devices—which permit good access to the patient—are often used. So-called c-arm systems, in which the x-ray tube and detector are arranged on the arms of a c-arm, which may be freely positioned around the patient, are favored in this case, said arms being situated opposite to one another. Even with such c-arm systems, tomographic images of the patient can be generated if necessary since the c-arm can likewise be positioned around the patient by approximately 180°.
By injecting a contrast agent, x-ray tomography can also be used to show tissues which, in their normal absorption behavior, are not distinguishable from their environment. If two rotations are carried out, with contrast agent being administered in only one rotation, and the image series then being subtracted from one another, the contrasted tissue, for example a vascular tree, can be reconstructed in isolation. This method is known as 3D subtraction angiography.
For the purpose of the reconstruction a large number of images is required from a rotation of at least 180°. Since the duration of the rotation is in the region of seconds (currently approx 4 to 8 seconds), physical functions such as heartbeat or respiration may result in localized blurring of the images, similar to motion blur such as is known from conventional photography.
Some physical functions can be recorded by simple methods and can be taken into account in the reconstruction. Such methods are described in DE 10 2004 057 308 A1.
A time-resolved representation of physical functions or of another time-dependent process has hitherto not been provided.
DE 196 22 075 A1 discloses a method and a device for the radiological investigation of individual cardiac phases of a patient, in which an x-ray beam bundle, which penetrates the heart of the patient in various angular positions within one half up to several rotations of the x-ray beam bundle around the patient, meets a beam receiver, wherein the cardiac rhythm of the patient is used to influence the rotation time of the x-ray beam bundle around the patient and to generate different control signals that are synchronized to the cardiac rhythm of the patient, so that radiological recordings of projections of different cardiac phases are possible.